Initially, a main object of a turbocharger (a turbine-type turbocharger) which is mounted on a commercially available automobile is to increase output of an engine having a relatively large displacement. However, from the viewpoint of an environmental protection, a demand for a turbocharger increases in order to compensate for output of an engine having a small displacement as a tendency toward an automobile having a small displacement increases. Meanwhile, it is preferable to decrease so-called specific turbo lag of a turbo vehicle.
In order to decrease the turbo lag, decreasing weight of an impeller of a turbocharger to decrease inertia moment is effective, and until now, adoption of a ceramic material in which weight can be significantly decreased compared to a metal material is reviewed, and, as described in PTL 1 and PTL 2, adoption of a fiber-reinforced resin is also reviewed.